There is known a head-up display device as an information display device of an automobile or the like.
Japanese Laid-Open Patent Publication No. H6-115381 discloses a head-up display device using a concave mirror as a turning mirror that can vary a position of a virtual image by varying a distance between a display as an object point and the concave mirror within a range allowing a virtual image point mirrored by the concave mirror to appear, in a manual manner or an automatic manner, or in a combination of these manners.
Japanese Laid-Open Patent Publication No. 2009-150947 discloses a vehicle head-up display device that includes a light source, a scan unit that scans light from the light source in a two-dimensional manner, a screen on which an image is formed by scanned light, and a projection unit that projects the image on the screen, and that varies a distance between the projection unit and the screen to vary a position of a virtual image projected.